Specific scent glands and other biological sources of odors are widespread in the animal kingdom. Olfactory stimuli from these sources elicit specific behavioral and neuroendocrine responses. Individual components of a particular behavioral sequence may depend upon different individual compounds within a single melange of natural odors. They may also depend upon only a portion of the available sensory apparatus (i.e. the main or accessory olfactory system). The glandular sources of natural odors and the behavioral responses to them are often modulated by endogenous hormone levels and in some cases by environmental variables. There are several broad questions to be answered about the mechanisms of olfactory communication in mammals including: (1) Which chemical compounds are active in natural scents? (2) How do natural scents activate the main and accessory olfactory organs? (3) Are there special modes of activation for behaviorally important odors like pheromones or (4) Are all odorants treated in the same way regardless of their import? (5) Once the system has been activated, are there distinct coding mechanisms which operate in selected anatomical regions for particular classes of odors? (6) What is the functional neuroanatomy of the main and accessory olfactory systems especially those areas concerned with the perception of pheromones? (7) What are the relative contributions of olfactory and other sensory signals in modulating mating and other natural behaviors? and (8) How are the various chemosensory systems coordinated to eventuate in a complex olfactory guided behavior such as mating? The hamster will be the primary model because it has well recognized sources of natural scents, several of which are partially characterized chemically. It has specific scent marking behaviors for the deposition of these scents and easily measured behavioral responses to their perception, all of which are under the control of endogenous hormones. Chemical, anatomical, behavioral and physiological techniques will be utilized at appropriate levels of the main and accessory systems in order to answer the above and related questions about olfactory communication.